The present invention is described for a memory card. However, the present invention may in general be used for any type of semiconductor device card.
FIG. 1 shows a memory card 102 of the prior art for transmission of data between a memory device 104 and a host 106. The memory card 102 is inserted into the host 106 that provides a host voltage to the memory card 102. The host voltage from the host 106 is coupled to a memory controller 108 and the memory device 104. In such a manner, such components 104 and 108 of the memory card 102 derive power from the host 106 for operation.
In the prior art, the memory device 104 operates properly when the working voltage of the memory device 104 is substantially same as the host voltage from the host 106. For example, the host 106 and the memory device 104 both operate with a working voltage of 3.3 Volts.
Unfortunately, the prior art memory card 102 cannot be used with a host providing a different host voltage from the working voltage of the memory device 104. Thus, in the prior art, the host 106 operates properly with the memory card 102 when the memory device 104 has a substantially same working voltage as the host voltage. Conversely, the memory device 104 operates properly when interfaced to the host 106 providing substantially the same host voltage as the working voltage of the memory device 104.
Recently, the memory device 104 is designed with lower working voltage such as 1.8 Volts for example for minimizing power dissipation. However, such a memory device 104 with reduced working voltage would not operate properly with a host 106 providing a higher host voltage.
U.S. Pat. No. 5,828,892 to Mizuta (hereafter referred to as “Mizuta”) discloses a memory card 11 having a power source voltage control circuit 12 that provides a desired working voltage to an I/O (input/output buffer) 13 and a DRAM (dynamic random access memory) device 14, as illustrated in FIG. 2. The voltage control circuit 12 provides the desired working voltage (such as 3.3 Volts for example) even when the host voltage Vcc is higher (such as 5.0 Volts for example).
FIG. 3 shows the implementation of the voltage control circuit 12 as disclosed in Mizuta. The host voltage is received at an input 28 that is coupled to a first window comparator 21 and a second window comparator 24. The first window comparator 21 turns on a first MOSFET 22 if the host voltage is within a first range of values such as 4.5 Volts to 5.5 Volts. The second window comparator 24 turns on a second MOSFET 25 if the host voltage is within a second range of values such as 3.0 Volts to 3.6 Volts.
The first MOSFET 22 that is turned on couples the host voltage to a DC-DC converter 23 that converts the host voltage in the first range of values down to the working voltage of the DRAM 14 (such as 3.3 Volts for example). Such as stepped down working voltage is generated on an output terminal 29. The second MOSFET 25 that is turned on simply couples the host voltage in the second range of values to the output terminal 29 as the working voltage of the DRAM 14.
Thus, the voltage control circuit 12 provides the working voltage that is lower than or equal to the host voltage. Consequently, the memory card 12 may be used with different types of hosts providing host voltages that are greater than or equal to the working voltage of the DRAM 14.
The memory card 11 of Mizuta accommodates different host voltages to operate with different types of hosts. However, the memory card 11 of Mizuta accommodates a predetermined working voltage of the memory device 14 as the DC-DC converter 23 is fixed for conversion to the predetermined working voltage. With advancement of technology, the working voltage of the memory device 14 may be decreased further and further. Thus, the memory device within a memory card may have one of various working voltages. However, the memory card 11 of Mizuta does not accommodate various working voltages of the memory device 14.
Thus, a memory card that is easily adaptable for various working voltages of the memory device is desired.